Potentiometer resistance



Juy H, lfii'l. 1. EERMANN POTENTIOMETER RESISTANCE Filed May 19, 1930 Patented July 11, 1933 UNTED STATES PATENT LOUIS BERIWIANN, OF MELROSE IAR-K, ILLINOIS, iSSIG'OR ELEGRGAL ENGINEERS EQUIPMENT CO., OF MELROSE PARK, ILLINOIS, CCR2-PGR POTENTIOMETE OI* ILLINOIS R- BESESTNCE Application led May 19, 1930. Serial Nec 453,680.

This inventionv relates to potentiometers, more particularly to wire wound potent-iometers, either low or high resistance and of suitable current carrying capacity.

In the control of the volume of radio sets, in television equipment, in X-ray equipment, in photometric work and in other scientific measurement work, potentiomete are generally employed. It is essential in such cases to have a straight line stepless resistance -unit of re sonable In the prior Patent No. 1,680,744, issued to Alfred F. C. Lotz, August 1l, 1928, is disclosed a rheostat consisting of two drums or cylinders having threaded external surfaces and disposed with their axes substantially parallel. A resistance wire is wound from one drum to the other to vary the resistance of the external circuit, in a manner which will be best understood `from a perusal oit this patent.

In mypresent invention, I alter the design oit' a rheostat of this same general class to make it into a potentiometer, the alterations consisting principally in providing a third contacting element located substantially mid way between the two drums and over which the wire ot the resistance unit is passed as it is unwound from one drum and wound onto the other. Both drums are ycomposed of an insulating material and electrical connections to the unit are made in such a manner that the entire length of the resistance wire is Lalwaj, s in one of the electrical circuits through the unit. The position of the auml" iary contact arm relative to the ends oi the. wire alters the resistance between that arm and the ends of thewire, thereby securing the resistance variation commonly secured in socalled potentiometers.

Other advantages of my invention not specilically mentioned here will be apparent from a reading of the detailed description and claims which follow.

Now, in order to acquaint 'those skilled in the art with the construction and operation ci a device embodying my present invention, I shall describe in connection with the accompanying drawing a particular embodiment of the invention.

along the line igure 2, looking in the direction of tee ari nrs;

TFigure is eros ctional view taken along the hne l et gare 2, looking in the direction the arrows;

Figure 5 is a. cross sectional View tal'en along the line 5 5 o'l Figure 3, looking in thc direction oi" the arrows; and

Figure (i is cross sectional 'flew taken along the line G-t of Figure SE, looking in the direction ot the arrows:J o i To illustrate e re.v 'ive dimensions of a commercially pi JYical embodiment of my in- 70 yention, the dei. Ace shown in the accom aanving drawing a substantially full size oi' that device. This is .i crely illustrative and is in no wise in ended 1 limt the size or proportions of the inve Referring to th closed with walls con i .s I taken on the line 2 2 55 n y or l. igure E .e operating linob;

1. Iligure S :tional vienT taken t im e c ione oi detachable c The `walls o and l. v'. 1 ong, nit! hen. ends rounded .1. a u l i 1l Y l or senmcnctn u., cati end o and o having a 1 h may co1n} )ri. 1 i a 85 i Jftiyeify l; 1 trip ot transparent lexrainne, esilnloig` isniglass (tri. s i as`^fr .c lf-,e form or lit within .nanfiiig' iiiduwdith C l 1 I i c rh opposite or tree ends or overlapping. The opposite edges c.. the cover 10 within the ilanges 7, se that tno cover is held vHrmlv and properly in 1; ce by the means which holds the end walls 5 and G together.

lotatably monnted within tlie cover l() and between the end walls 5 and G with their axes substantially parallel are insi'llatino cylinders or orums l2 and 13. n

The cylinder 12 may be formed o't insulating material., such as a phenol condensation 10o product, and it comprises an axially bored hub 14: and a. surrounding cylindrical wall 15 having an open end and a closed end 17. Integral webs 18 may be provided between the hub 14 and the wall 15. The cylinder 12 is rotatably ournalled upon a shaft 19, the opposite ends of which are reduced to provide shoulders which abut and space the end walls 5 and 6. The reduced ends of the shaft 19 are threaded and these threaded ends extend through openings in the end walls and 6 and engage in nuts 20, which, when tightened or brought up, clamp the end walls 5 a. d 6 lirmly together. Suitable washers may be interposed between the end walls 5 and 6 and the nuts 20, as shown. The cylinder 12 is thus mounted to rotate on the shaft 19, and the shaft 19 is rigidly secured in the case and spaces and oins the end walls thereof.

The cylinder 13 is preferably also formed of insulating material, such as a phenol-condensation product, and it comprises an axially bored hub 24- and a surrounding cylindrical or annular wall 25 having an open end 26 and a closed end 27. The wall 25 is provided internally with a longitudinally extending integral lug or shoulder 28, and the hub 24 terminates short of the open end of the cylinder 13. The cylinder 13 is rotatably journalled upon a shaft 29, the opposite ends of which are reduced to form shoulders which abut and space the end walls 5 and 6 symmetrically upon opposite sides of the driving shaft 30. As with the shaft 19, the reduced ends of the shaft 29 are threaded and these threaded ends extend through openings in the end walls 5 and 6 and engage in nuts 32 which clamp the end walls 5 and 6 firmly together. As before. suitable Washers are preferably interposed be tween the ends 5 and 6 and the nuts 32. The cylinder 13 is thus mounted to rotate on the shaft 29, which shaft 29 is rigidly secured in the case, and with the shaft 19 provides a symmetrical spacing and joining of the ends 5 and 6.

The closed end 17 of the cylinder or drum 12 has an annular recess 35 in which is secured a metallic annular contact or eommutator ring 36, which ring is preferably composed of brass or other noncorrosive metal. The closed end 27 of the cylinder or drum 13 is also provided with an annular recess 27 in Which is secured a metallic annular contact or commutator ring 36 of the same metal as the ring 36.

The resistance element comprises a strand or strands of resistance wire 37, preferably an alloy' of nickel, or the like. One end of this Wire or conductor 37 is wrapped on the drum 12 with its adjacent end turned in through a. slot or recess 38, and is Welded, soldered or otherwise connected electrically and mechanically to the ring 36 at 39.

The opposite end of the conductor 37 is Wrapped upon the cylinder 13 with its end turned in through a radial yopening 40 and extended downwardly at 42 along the inside edge of the wall 25 and is welded, soldered or otherwise connected electrically and mechanically to the ring 36 at 37. The external surface or periphery of the insulating cylinder 12 is threaded or grooved spirally at to accommodate the turns of the wire 37, and to space and insulate them from each other. The external surface or periphery of the insnlatinfr cylinder 13 is similarly threaded or grooved spirally at 44 in the .saine direction, so as to accurately arrange the turns of the wire 37 thereon, and to guide the wire properly to and from the cylinder 12.

t one end the wire 37 preferably has a dead turn or two on the drum 12, that is, a turn or two which remains on the drum in the complete unwrapped position of the drum, and at its opposite end the wire 37 preferably has a similar dead turn or two on the drum 13. This provides belt friction between the respective drums and the opposite ends of the conductor 37 and relieves the joints or connections of the terminals of the wire 37 with the rings 36 and 36, respec tively, of any stresses at the limits of rotation of the drums. f

The opposite ends of the wire 37 have terminals or circuit connections for connecting the device serially or otherwise in the desired circuit. These connections comprise spring Contact or brush arms i8 and 50. One of these arms is secured to the end wall 6 by a screw 52 which extends through and engages in a nut 53 which, with an additional nut 5l, provides a binding post to which the desired circuit c-onductor may be conveniently connected mechanically and electrically. The mounting of the other contact arm upon the end wall 6 and its circuit connection are substantially the same. Spring washers 55 are preferably interposed between the end 6 and the nuts 53 to keep the contact arms tightly clamped to the back or cover 6.

The contacting ends of the arms 48 and 50, which have wiping contacten the rings 36 a nd 36, respectively, are preferably split or divided longitudinally at 58 to form spring ends for good, firm and maximum contact with the rings 36 and 36 at all times.

The contact arms L18 and 50 are mounted with their lengths extending longitudinally of the back 6 and preferably with one disposed on each side of the driving shaft 30. This provides a compact and symmetrical arrangement. The arms 4-8 and 50 are carried by the back 6 and removed and assembled therewith.

The arms are preferably prevented from rotating about their screws by boss or shoulder or in any other preferred manner.

For the purpose of firmly securing the rings 36 and 36 in the recesses 35 and 37, I tin the washers or rings 36 and 36', or coat them with a bearing bushing or sleeve 68.

and this reduced end is rotatably thereto a driving a suitable'relatively soft conducting coatinv. rlhe washers may be of brass, for example, and may be pressed into the recesses in the ends of the drums 12 and 13. This tinning or coating provides firm adhesion of the washers to the insulating drums 12 and 13, and it provides soft contact surfaces, which, upon operation of the device, I find are quickly grooved bythe contact arms 48 lor 50, this grooving of the arms thereinto forming good, maximum contact at all times. Subsequent hand tinning for connection of the wire 37 to the rings is also thereby avoided.

rlhe driving shaft 30 extends between the cylinders lor drums 12 and 13, which makes for compactness and symmetry. The inner or back end of the shaft 30 is reduced at 65 j ournaled in the back cover wall 6. The forward part of the shaft 30 is enlarged at 66 and the enlarged shaft part 66 is rotatably journaled in The bushing 68 comprises an externally threaded cylindrical sleeve or thimble having an enlarged noncircular head 70 of square or other polygonal formation, for example, which may be formed integral with the bushing sleeve. The inside surface of the wall 5 has a non-circular recess 72 conforming to the head 70 and adapted to receive or accommodate same, the engagement of the head 70 in this recess 72 holding the bushing rigidly against turning in the wall 5 and limiting its forward or outward movement therethrough. A nut 73, threaded externally upon the bushing 68 and against the wall 5, binds the bushing rigidly in said wall.

an additional nut 76 is provided on the threaded bushing 68 to thereby permit mounting of the unit upon a suitable panel in the customary single hole mounting method. 'll'ne outer end of the shaft 30 has an operating knob 78 for turning the shaft. This knob r'8 may be ofinsulating material with a grooved or knurled periphery and a. metal insert or sleeve 79 secured axially in the hub portion of the knob. The insert 79 is threaded to accommodate a radial screw 81 which threads through the sleeve 79 and into enoement with the shaft 30 to secure the knob gidly thereon.

Between the front cover or end wall 5 and the forward end of the cylinders or drums 12 and 13, the driving shaft 30 has secured gear or pinion 82. Preferably, this pinion 82 is floated on the siaft 30 in the manner described in detail in the Lotz Patent No. 1,680,744, issued August 14, 1928,although othersuitable means of attach- `ment may be substituted therefor.

The driving pinion 82 is disposed between and meshes with a pair of gears 86 and 87, one for each of the cylinders or drums 12 and 13, the particular gear ratio shown being substantially two to one, the drums performing one revolution for each two revolutions of the gear 82 or main shaft 30. The gear 86 may be formed by cutting the teeth directly in the end of the cylindrical insulating wall 15 of the drum 12, which makes a rigid integral unit in which attachment means or connections between the gear and drums are eliminated.

As shown in Patent No. 1,680,744, the gear 87 has an axially bored hub loosely rotatable on the shaft 29, and projecting from the inner surface of the gear is a driving lug 89 which is preferably formed integral with the gear. Disposed within the cylinder 13 and coiled about the hub 2/1- is a helical. ton-- sion spring 90. One end of this spring turned out at 91 into ei'igagement with the lug` 28 formed integral with the closed end 27 of the drum 13. The opposite end is turned out at 92 for engagement or co-operation with the lug 89, providing a yieldable or take-up connection between the drum 13 and the gear 87, for maintaining the resistance wire 37 always properly tensioned or tightened.

The main shaft 30 is threaded at 95 and if desire-d a rider 96 may be threaded thereon to limit the rotation of the knob 78 to 'thereby prevent tearing the wire 37 loose from the drums 12 and 13. The operation of this rider iamore fully brought out in priorPatent No. 1.680,74-1. In the present invention the rider does not disengage the contact springs from the plates 36 and 36 to open the circuit when it is in its innermost position, but rather merely wedges against the back wall 6 er the pinion 82, to prevent further rotation of the shaft.

The potentiometer is used in an electrical circuit in which the contact arms 50 and 4.8 are connected to lixed points inthe circuit through wires extended to the binding post 52, these connections being permanently and alterably made. The third or auxiliary contact of the potentiometer comprises bindino' post 100 permanently connected to a metall plate or bar 101 which engages the wirer 37 midway between the drums 12 and 13. Vhen the potentiometer is turned so that all the wire is wrapped on the drum 12, for example, the resistance between the bindingl post 100 and the left hand binding post 52, Fi gore 3, will be the resistance of that wire w il. permanently remains upon the drum 13. As the knobI 78 is turned to unwrap the wire from the drum 12 and wrap it onto the drum 13, the resistance between these two binding posts increases as the amount of wire on the drum 37 increases. Conversely when all of the wire is on the drum 12, the resistance between the terminal 100 and the right hand terminal 52, Figure 3, is at its maximum, and that value of resistance is decreased as the knob is turned to unwrap the wire therefrom and to wind it on the drum 13.

The contacting plate 101 is preferably of rectangular cross section, and composed of a spring like material such as spring brass, spring bronze, or other suitable metal, and is tensioned to exert a pressure outward on the wire 37 so that that wire is always in good electrical contact with the strip 101. The movement of the wire across the surface of the strip 101 tends to wipe any dust or corrosion that may accumulate on the strip oli' of it, so that a good electrical contact between the wire and strip is thereby assured. he surface of the wire is likewise kept clean, "so that in the operation oit the potentiometer the resistance value between the central terminal and end terminal 52 can be changed noiselessly at all times.

' rthus it will be seen that by suitable choice ol the size and composition of the wire 3T the potentiometer may be made to any prescribed value o't resistance, the unit so constr cted being compact and stiiidily built. he operation is simple and a wide range o't resistance variation can be obtained through the instrument.

lVhile l have chosen to show a preferred embodiment of my inveni'iion, l have done so by way ot example only, as there are many modifications which can be n'iade by one skilled in the art without departing from the teachings oli my inif'eiition. to be limited only bythe scope of the ap pend-- ed claims.

that is claimed is:

1. ln a potentiometer, a pair of cylindrical drums disposed with their axes parallel, a resistance wire wound on said drums and extending therebetween, one end of said wire being rigidly attached to each of said drums, means for making an electrical connection to each end of said wire, means for rotatingl said drums simultaneously to wind said wire from one to the other, and resilient, yielding` stationary means 'for contacting with said wire as it passes from one orum to the other.

2. In a potentiometer, a pair of cylindrical drums disposed with their axes pai-alici, a resistance wire wound on saifl drums and extending therebetween, one end oit said wire being rigidly attached to each of the drums, means for making an electrical connection to I am therefore each end of said wire, means for rotating said drums simultaneously to Wind said wire from one to the other, and means consisting olf a stationary, resilient, yielding bar betii'een said drinns for contacting said wire as it passes from one drinn to the other.

3. l'n a potentiometer, a pair of cylindrical insulating drums disposed with their axes parallel, a resistance wire wound on said drums and extendingtherebetween, one end oi said wire being rigidly attached. to each o1" .'aid drums, means including a plate ataelied to the drinn and a stationary linger engaging said plate tor making an electrical conneciiion to each end of said wire, means :tor rotating said drums simultaneously to wind said wire VItroni one to the other, and stationary, resilient, yielding means for contacting with said wire intermediately oi its ends as it p; esos trom one drinn to the other. si. ln a potentiometer, a pair of insulating p llanges on said plates, a pair ot shouldered shafts disposed between said plates and holding them together with said flanges adjacent, a housinginember disposed between said plates and held in place by said flanges, a pair ot insulating drums one -niounted on nach ot said shalts, a resistance wire having an end attached to cach of said drums and extending therebetween, stationary contacting means mounted on one of said plates and engag n:ig a cooperating means on said drum to establish electrical connections with the ends of said wire, means on the opposite side ot said plate 'tor establishing an electrical connection with said connecting means, a third stationary, resilient, yielding connecting means mounted on said plate and engaginfI said wire between said drum intermedii y ol its ends, means on the opposite side oi. said plate for establishing an electrical connection with said third contacting meinber, and means mounted on the other plate for simultaneously rotating said drums to wind said wire on one of them while iinii'inding it iti'oin the other, to thereby vary the resistance between said third contacting means and said pair of contacting means. Y

in witness whereof, l hereunto subscribe my name this 1Q day oli May, 1930.

LOUIS BERMANN. 

